Anhydrous Ba${{O}_{2}}$ is not used for preparing ${{H}_{2}}$${{O}_{2}}$. Why?

BaS${{O}{4}}$ formed during the reaction of Ba${{O}{2}}$ with ${{H}{2}}$S${{O}{4}}$ forms a protective layer around unreacted Ba${{O}_{2}}$ and the reaction stops after sometime.